In the formation of integrated circuits (IC's), it is often necessary to deposit thin films or layers, such as films containing metal and metalloid elements, upon the surface of a substrate, such as a semiconductor wafer. One purpose of such thin films is to provide conductive and ohmic contacts in the circuits and to yield conductive or barrier layers between the various devices of an IC. For example, a desired film might be applied to the exposed surface of a contact or via hole on an insulating layer of a substrate, with the film passing through the insulating layer to provide plugs of conductive material for the purpose of making inter-connections across the insulating layer.
One well known process for depositing such films is chemical vapor deposition (CVD) in which a film is deposited using chemical reactions between various constituent or reactant gases. In CVD, reactant gases are pumped into the processing space of a reaction chamber containing a substrate. The gases react in the processing space proximate the substrate, resulting in one or more reaction by-products. The reaction by-products then deposit onto the substrate to form a film on the exposed substrate surface.
Another variation of the CVD process which is widely utilized is a plasma-enhanced CVD process or PECVD process in which one or more of the reactant gases is ionized into a gas plasma to provide energy to the reaction process. PECVD is desirable for lowering the temperatures that are usually necessary for a proper reaction with standard CVD. In PECVD, electrical energy is delivered to the gas or gases to form and sustain the plasma. For one such PECVD process, the susceptor containing the substrate and a planar element in the processing space, such as a gas supply element, are electrically biased to operate as RF electrodes for energizing one or more of the reactant gases into an ionized plasma. Such a method is commonly referred to as a parallel plate method because the susceptor and the other biased planar element are maintained generally parallel to one another to simulate biased electrical plates with the substrate positioned therebetween and parallel to the biased elements.
The reactant gases for CVD and PECVD processes are delivered to the processing space and substrate through a gas delivery system which provides the proper flow and distribution of the gases for the CVD process. Generally, such gas delivery systems contain gas-dispersing elements in the reaction chamber, such as gas injector rings or flat showerheads, which spread the entering reactant gases around the processing space to insure a uniform distribution and flow of the gases proximate the substrate. Uniform gas distribution and flow is desirable for a uniform and efficient deposition process, a dense plasma, and a uniformly deposited film. Since the gases utilized in CVD and PECVD processes are reactive, it is often necessary to use a separate dispersing element for each constituent gas in order to keep the gases segregated or unmixed prior to the processing space. Otherwise, if the gases mix prior to the processing space, premature deposition occurs inside the dispersing element and inside other sections of the gas delivery system, which hinders a uniform flow of the gas, degrades the deposition process and may contaminate the deposited film.
To maintain separate constituent gases, multiple, concentric gas injector rings have been utilized to prevent premature mixture and deposition prior to the processing space. However, multiple gas injector rings in the processing space make it difficult to utilize PECVD techniques because the rings interfere with the placement and action of the RF electrodes necessary for such PECVD techniques. Therefore, the rings detrimentally affect plasma generation.
Conventional RF PECVD processes generally utilize a biased, planar gas showerhead opposite a parallel, biased susceptor. One such PECVD process and apparatus is disclosed in U.S. Pat. No. 5,547,243, which is commonly owned with the present application. While such a technique produces suitable PECVD films, directing and dispersing all of the reactant gas constituents through available showerheads will produce premature mixing of the gases before the processing space and yield undesirable deposition inside of the showerhead, or in-line in the system before the showerhead. Therefore, for parallel plate PECVD, it has been necessary to disperse some gases through inlet ports other than the showerhead, yielding non-uniform flow of some of the gas constituents at the substrate, or interfering with plasma generation.
Accordingly, it is an objective of the present invention to reduce and generally prevent the premature mixture of reactant gases in CVD and PECVD reactions.
It is still another objective of the invention to prevent the deposition of film material in the gas delivery system and to provide a uniform flow and distribution of reactant gases to the processing space for the deposition process.
It is another objective of the invention to maintain the separation of the reactant gases and generally prevent their interaction until they are injected and mixed proximate the substrate.
It is a further objective generally to prevent such premature interaction and deposition in a PECVD process utilizing parallel plate electrodes without interfering with the RF plasma generation.
Accordingly, the present invention addresses these objectives and the shortcomings of the various CVD and PECVD apparatuses and processes currently available in the prior art.